High tensile multi-layer cylinder



May 5, 1964 J. .1. CHYLE HIGH TENSILE MULTI-LAYER CYLINDER Filed July 26. 1960 N as Ins

fin V. B

United States Patent 0 3,131,725 HIGH TENQIE MULTi-LAYER YLENBER John J. Chyle, Wauwatosa, Wis, assignor, by mesne assignments, to Chicago Bridge is; iron Company, Oak Brook, iii, a corporation of iiiinois Filed July 26, 1960, Ser. No. 45,420 2 Qlaims. (iii. 133-440) This invention relates to a high tensile multi-layer cylinder for use wherever very high internal fiuid pressures are to be retained.

in the fabrication of pressure vessels the use of multilayer steel cylinders has been known for some time and the advantages have been well established. In commercial practice only cylinders of the type wherein each layer is itself cylindrical have found favor. Cylinders employing coil wrapped layers have not found favor.

The expired Stresau Reissue Patent No. 22,251 is illustrative of the first type and has been the subject of substantial commercial operations. Other patents such as the expired Raymond Patents No. 2,268,961, 2,273,- 736, and 2,331,504, may be considered generally representative of the coil wrapped structures.

Former workers in this field have always visualized the use of ordinary steels available in sheets of to in thickness and in sizes generally suitable for weld fabrication. Because of the stifiness of such sheets it has been generally easier to form them in a roll prior to application to the structure being fabricated, rather than to attempt forming them into the desired curvature in situ and by wrapping processes.

The present invention is based upon the concept that the coil wrap process provides a means for rapidly constructing vessels of much thinner layers and of substantially thicker total wall thickness. The invention proposes to make cylinders of any practical diameter and wall thickness by coil wrapping paper thin sheets or strips of very high tensile strength metal.

The accompanying drawing illustrates a high pressure cylinder of the character embodying the present invention. In the drawing the single figure illustrates a cylinder with parts broken away and sectioned to show the construction.

In the drawing the cylinder 1 is'shown as comprised of a large number'of very thin spirally wrapped thin layers 2 of metal, as described hereinafte Cylindrical sections as illustrated may be secured end to end, or closed at the ends as may be desired to make a high pressure vessel. The thickness of the wall will be determined by the strength of the metal, the diameter and the stress condition of the cylinder.

It has not been possible heretofore to provide large cylinders of metal having tensile strength in excess of about 105,000 pounds per square inch and up to and in excess of 150,000 pounds per square inch tensile strength. Such high strength metals in thicknesses greater than about i are generally of low ductility and difiicult to form into cylindrical shape without encountering crackmg.

The present invention overcomes this difiiculty and permits fabrication of very high tensile strength metals by employing paper thin sheets or strips of the metal. These have been found to be formable as by wrapping into coiled cylinders of substantial diameter. Thicknesses of the order of .03 to .04 inch are suitable for metals having a tensile strength of the order of 150,000 pounds per square inch obtained as by heat treating or cold working prior to fabrication. For higher tensile strength metal thinner sheets or strips should be employed, and it is conceivable that metal foils may be used in some instances.

By employing the present invention, instead of the usual three to four layers of metal per inch of wall thickness in present day multi-layer cylinders, the cylinders will have generally in excess of twenty-five layers per inch of thickness, and instead of the usual tensile strengths of less than about 100,000 pounds per square inch obtained in present day cylinders of multi-layer constructed of reasonably low carbon steel, the cylinders of the invention will have tensile strengths of the order of 150,- 000 pounds per square inch and even higher as may be obtainable by specially heat treated high carbon steels or alloys capable of rolling to the thinnesses referred to prior to such heat treatment.

Depening upon the availability of wide sheets of the material capable of welding edge to edge, the cylinders may be constructed of a length corresponding to the width of the sheet with the latter coil wrapped in the formation of the cylinders. Where the material can be obtained only in strips of less Width than the desired length of the cylinders, it is possible to spirally wrap strips upon the inner mandrel or core, as in the wrapping of spiral pipe.

Where it is desirable to weld cylinders end to end or adjacent strip edges to each other, this may be done by processes designed to produce joints of the same high tensile strength as the metal of the stock.

One of the advantages of the wrapping process of making the multi-layer cylinders of the present invention lies in the fact that welding may be reduced to a minimum by avoiding practically all longitudinal seam welding except for the start and finish and any necessary end to end sheet or strip welding.

It is possible to wrap with substantial tightness to prestress the cylinders and thereby place the inner portion of the cylinder wall under initial compressive stresses and the outer portion under initial tensile stresses, somewhat as indicated in US. Patent No. 3,098,620 granted to Fred A. Carstens, the application of which was copending herewith.

The accompanying drawing illustrates diagrammatically a coil wrapped cylinder of the present invention constituting the best mode presently contemplated for carrying out the invention.

Referring to the drawing, the cylinder 1 is composed of an inner retaining cylindrical metal core 2 having coil wrapped thereon a paper thin metal sheet 3 in a large number of successive convolutions to provide the desired wall thickness for the cylinder.

The core 2 may be a cylinder fabricated from a plate of approximately one quarter inch thickness and a metal capable of forming into the cylinder with the meeting longitudinal edges welded together as at 4. In general the metal of core 2 should be a low carbon steel that can be readily formed in whatever thickness is obtained.

The coil layers of sheet 3 are constructed by tightly wrapping the sheet upon the core 2 until the desired wall thickness is provided for the cylinder. Where the pull exerted in wrapping sheet 3 substantially stresses it as it is applied to the cylinder, it is possible to produce a final cylinder wherein core 2 and inner layers of metal adjacent thereto are under initial compression stress effected by an initial tensile stress in the outer layers.

The sheet 3 is preferably of a steel which can be rolled at the mill in suitable widths and to a thickness substantially less than inch, such as to a thickness of the order of .03 or .04 inch. The thinner the better. It then should be capable of substantial increase in tensile strength by suitable heat treating processes as by heating to beyond the upper critical temperatures and rapidly cooling thereof to below the Ms temperature (the temperature at which martensite begins to form).

For this purpose steel conforming to the following composition range may be employed:

A typical composition (Specification 4405 of American Metal Society) is as follows:

C .40 Mn .70 Si .25 Cr .80 Ni l 80 Mo 25 V 10 When such a steel is heated to 1650 F. and subsequently quenched and tempered at 1000 R, the tensile strength will increase from approximately 100,000 pounds per square inch to approximately 200,000 pounds per square inch. At the same time the metal will become correspondingly less ductile. However, because the sheet is so thin its bending stresses in wrapping the same core 2 will be sufficiently low to avoid cracking from brittleness.

Various alloy steels may be employed to give desired characteristics. In general, it is believed that the present invention is the first to provide a high pressure cylinder having a wall of substantial thickness and of metal with a tensile strength exceeding 100,000 pounds per square inch.

One of the advantages in utilizing the coil wrap method of producing the cylinders is that welding is kept to a minimum. Longitudinal welds are only needed to secure the starting edge of the sheet to be coiled, and generally to secure the final end edge of the wrapped coil. Ali intermediate layer contact is frictionally tight to provide the desired flexibility and greater strength of multilayer construction as compared to solid wall cylinders.

It is possible to provide wall thicknesses of any extent whereas solid wall weld fabricated cylinders are usually limited to about six inches. By reason of the greater wall thicknesses possible with the present invention and the greater strength metal that can be used, the cylinders may be made substantially larger in diameter for the same internal working pressures, thereby providing desirable greater capacity.

By taking advantage of the higher tensile strength of the metal employed, the cylinders can be made of substantially less wall thickness for the same working pressures, thereby providing much lighter weight structures, a factor substantially important in missiles and rockets.

Sheets of the thickness indicated can be obtained in widths up to five feet or even more, and make it possible to construct cylinders of a corresponding length. Girth welds between abutting ends of cylinders, because of the fineness of the layers may be made as readily as in solid wall cylinders.

Various modes of carrying out the invention are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention.

1 claim:

1. A cylinder for incorporation in pressure vessels, rockets and the like for retaining high internal fluid pressures, comprising a tubular metallic cylindrical core of substantial thickness and rigidity reinforced by a coil wrapping of a plurality of layers of flexible metallic sheet material having a thickness less than about .04 of an inch and a tensile strength exceeding 100,000 pounds per square inch, said coil wrapping having its adjacent layers in tight frictional metal to metal contact throughout and having a total thickness several times that of said core, said core having a thickness several times that of said sheet material, the individual layers of said wrapping being generally unattached to each other between the ends thereof, and welds maintaining the layers in tightly wrapped relation.

2. A cylinder for incorporation in pressure vessels, rockets and the like for retaining high internal pressures, comprising a tubular metallic cylindrical core of substantial thickness and rigidity reinforced by a coil wrapping of a plurality of layers of flexible metallic sheet material having a thickness less than about .04 of an inch and a tensile strength exceeding 100,000 pounds per square inch, said coil wrapping having its adjacent layers in tight frictional metal to metal contact throughout and having a total thickness several times that of said core, said reinforcing having the outer convolutions thereof under resi'ual tensile stress placing the core under residual compression stress, said core having a thickness several times that of said sheet material, the individual layers of said wrapping being generally unattached to each other between the ends thereof, and welds maintaining the layers in tightly wrapped relation.

References Cited in the tile of this patent UNITED STATES PATENTS 2,268,961 Raymond et al. Jan. 6, 1942 2,332,462 Nilson Oct. 19, 1943 2,359,446 Scudder Oct. 3, 1944 2,363,967 Jasper Nov. 28, 1944 2,372,723 Jasper Apr. 3, 1945 2,914,091 Barnes et al. Nov. 24, 1959 2,933,214 Douyard Apr. 19, 1960 2,982,457 DAlelio May 2, 1961 

1. A CYLINDER FOR INCORPORATION IN PRESSURE VESSELS, ROCKETS AND THE LIKE FOR RETAINING HIGH INTERNAL FLUID PRESSURES, COMPRISING A TUBULAR METALLIC CYLINDRICAL CORE OF SUBSTANTIAL THICKNESS AND RIGIDITY REINFORCED BY A COIL WRAPPING OF A PLURALITY OF LAYERS OF FLEXIBLE METALLIC SHEET MATERIAL HAVING A THICKNESS LESS THAN ABOUT .04 OF AN INCH AND A TENSILE STRENGTH EXCEEDING 100,000 POUNDS PER SQUARE INCH, SAID COIL WRAPPING HAVING ITS ADJACENT LAYERS IN TIGHT FRICTIONAL METAL TO METAL CONTACT THROUGHOUT AND 